Spiel convention in Essen, Germany - how quickly does it sell out?

We're planning on going to Essen, Germany for the Spiel convention (largest board game convention in the world.) I'm trying to figure out if we can begin making flight and accommodations bookings before purchasing the convention tickets in July. Does anyone know how quickly tickets to the convention sell out (or if they ever sell out?) Can we safely make other trip bookings before we get the tickets? Thanks in advance!